Polyvinyl alcohol fibers

ABSTRACT

1. POLYVINYL ALCOHOL FIBERS COMPRISING AN ESSENTIALLY WATER ISOLUBLE POLYVINYL ALCOHOL HAVING AN AVERAGE DEGREE OF POLYMERIIZATION OF FROM ABOUT 1200 TO 3500 AND CONTAINING A RESIDUE OF BORIC ACID OR A WATER SOLUBLE BORATE SALT THEREOF IN AN AMOUNT OF FROM 0.2 TO 0.9% BY WEIGHT OF POLYVINYL ALCOHOL, SAID FIBERS BEING CHARACTERIZED BY A HALF-WIDTH OF (100) RELFACTION (B) OF 0.98 TO 1.40 AND AN IM/I30 OF FROM 0.40 TO 0.48 DERIVED FROM THE AZIMUTHAL X-RAY INTENSITY DISTRIBUTION AT THE ANGLE OF DIFFRACTION OF 19.2*.

United States Brent O" 3,850,901 POLYVINYL ALCOHOL FIBERS ShoichiTanaka, 550-1 Yasue; and Susumu Kousaka, 1273-4 Nakasho, both ofKurashiki, Japan; and Toshio Kirnura, 2-208 Katsuragi-cho, Nara, Japan NDrawing. Continuation-impart of abandoned application Ser. No. 90,816,Nov. 18, 1970. This application Nov. 7, 1972, Ser. No. 304,577

Claims priority, application Japan, Nov. 25, 1969, 44/ 94,790; Apr. 30,1970, 45/317,354 Int. Cl. C081? 3/34 US. Cl. 260-913 3 Claims ABSTRACTOF THE DISCLOSURE Polyvinyl alcohol fibers comprising an essentiallywater insoluble polyvinyl alcohol containing boric acid or a watersoluble borate salt thereof in an amount of from 0.2 to 0.9% by weightof polyvinyl alcohol, said fibers being characterized by a half-width of(100) reflection (B) of 0.98 to 1.40 and an I /I of from 0.40 to 0.48derived from the azimuthal X-ray intensity distribution at the angle ofdiffraction of 19.2".

This invention is a continuation-in-part of copending application Ser.No. 90,816 filed Nov. 18, 1970 and now abandoned.

The present invention relates to improved polyvinyl alcohol fibers. Moreparticularly, this invention relates to polyvinyl alcohol fibers whichexhibit excellent properties at high temperatures such as yarn tenacity,yarn initial modulus and yarn creep.

Generally, polyvinyl alcohol (PVA) fibers surpass other synthetic fibersin breaking strength and initial modulus, and have recently found wideuse in many fields, for instance, fiber reinforced plastics (FRP). It isa well-known fact that PVA fibers which are drawn to the drawable limitand minimized in heat-shrinkage exhibit outstanding breaking strengthand initial modulus. However, PVA fibers, like many other syntheticfibers, undergo a deterioration in properties at high temperature inproportion to the rise in the temperature.

The primary object of the present invention is to obviate the abovedeficiencies in synthetic fibers by providing a PVA fiber havingexcellent properties at high temperature. More particularly, thesynthetic fibers in accordance with the present invention are superiorto conventional PVA fibers with respect to yarn tenacity, yarn initialmodulus and yarn creep.

The PVA synthetic fibers of the present invention exhibit highcrystallinity and molecular orientation, and are characterized by thehigh temperature properties indicated below and by the amount of boricacid (H BO or a borate salt thereof contained therein, the properties athigh temperature being as follows:

Yarn tenacity at 120 C At least 7.5 g./d.

Yarn initial modulus at 120 C At least 100 g./d.

Yarn creep at 135 C Less than 2%.

Boric acid or borate salt content 0.2 to 0.9% by weight of PVA.

Generally speaking, the extensibility of synthetic fibers increases inproportion to the rise in temperature, and the strength and yarn initialmodulus decrease. It can be easily speculated that this phenomenonoccurs because movement is initiated in the molecular chain of the fiberin regions of low molecular orientation upon heating the fiber. Thismovement is soon transmitted to regions of the fiber where molecularorientation is intense. It is therefore important, in the improvement ofthe properties at high temperature of a synthetic fiber to suppress the3,850,901 Patented Nov. 26, 1974 movement of molecular chains as much aspossible. This can be achieved either by (1) intensifying theorientation of the molecular chains to such an extent as to prevent themfrom moving, or (2) adding to the polymer a material which hinders themovement of molecular chains. These two remedies, however, whenseparately employed are not capable of achieving the objects of thepresent invention, i.e., property improvement at high temperature suchas improvement in yarn tenacity, yarn initial modulus and yarn creep.For instance, improvement in yarn initial modulus may be expected in amethod wherein a conventional PVA fiber is subjected to post-treatmentwith boric acid; however, the same process will also result in aremarkable decrease in yarn tenacity.

It has been found in accordance with the present invention that theessential factor which fulfills the primary object of the presentinvention is a fibrous structure wherein the orientation of themolecular chains is quite intense as a whole but which contains asubstance to prohibit the movement of the molecular chains where themolecular orientation is relatively loose. That is, a portion or all ofthe boric acid or borate salt thereof contained in the fiber may combinewith the PVA in relatively loose orientation, to prohibit the movementof the molecular chains caused by heating. When the amount of boric acidor borate salt does not measure up to 0.2% by weight of PVA, it isinsufiicient to restrain the chain movement. When the boric acid orborate salt content exceeds 0.9%, it will prevent the molecular chainsfrom being highly oriented, thereby causing reduction of the yarnstrength.

The novel PVA fibers of the present invention comprise PVA having anaverage degree of polymerization of from about 1200 to 3500 andcontaining from 0.2 to 0.9 weight percent boric acid or a water solubleborate salt thereof, and preferably containing from 0.2 to 0.7 weightpercent boric acid or a water soluble borate salt thereof, said PVAfiber being characterized by a half width of reflection ([3) of 0.98 to1.40 and (T /I of 0.40 to 0.48 derived from the azimuthal X-rayintensity dis tribution at the angle of dilfraction of 19.2.

Among the structural parameters cited above characterizing the PVAsynthetic fiber of the present invention, the half width of (100)reflection ([3) is the param eter indicating the transverse magnitude ofcrystals in the fiber; whereas, the value of I /I denotes the structureof the amorphous region of said fiber.

It has now been found that a correlation exists between the advantageouscharacteristics of the PVA fibers of the present invention and thestructural parameters of such fibers. Thus, the PVA fibers of thepresent invention can be characterized by the two parameters describedabove as will be illustrated in detail hereinbelow.

vIn general, 5 peaks appear in the equatorial X-ray diffractionintensity curve of a synthetic fiber of PVA within the angles ofdiffraction ranging from 5 to 25, these peaks are designated, in orderof increasing angle of diffraction, as (100), (001), (101), (101) and(200).

The crystallographic significance of these reflections is discussed inthe literature: see, C. H. Bunn. Nature. 161, 929 (1948).

Crystals of PVA fiber comprise unit cells having a monoclinic crystalform characterized by: a=7.81 A., b=2.52 A., c=5.5l A., ac( anglebetween a and c axes)=9l 42, and in the case of a heat drawn fiber, theb-axis orients along the fiber-axis direction.

The planes of (100), (001), (101), (101) and (200) are parallel to theb-axis, oriented in the parallel direction to the fiber axis and soappear on the equator on X-ray diffraction.

The sharpness of the reflections of these planes parallel to the b-axisrelates to the width of the crystals, with the broader Width crystalsbeing considered the finer crystals; whereas, the (020) reflection is inthe plane perpendicular to the b-axis which relates to the length of thecrystals.

The value of the half width of the (100) reflection (,8) in the PVAfiber of the present invention ranges from 0.98 to 1.40, beingconsiderably broader as compared to conventional PVA fibers having ,8values of from 0.60 to 0.98. Consequently, the PVA fibers of the presentinvention have considerably smaller crystal width in the crystallinestructure in comparison to conventional PVA fibers.

The intensity distribution determined along the azimuthal direction atthe angle of diffraction of 19.2 has heretofore been found by C. H. Mac.Gillarry to represent the orientation of the amorphous region of the PVAfiber; see, Recueil des Travaux Chimiques des Pays-Bas T69, 3( 1950).The intensity at the meridian in the intensity distribution along theazimuthal direction of the fiber according to the present invention hasbeen found to be weaker than those of conventional PVA fibers. Near theequator, the intensity is affected by the effect of the crystallinereflection, and so the ratio of the intensity at the meridian to theintensity at the azimuthal angle of 30 has been adopted as a parameter(I /I characteristic of the fibers of the present invention. The smallervalues of said parameter signify less disorder in the amorphous regionof the fiber, and indicate better orientation of the molecular chain insaid amorphous region.

The PVA fibers of the present invention exhibit a value of the parameter(I /I ranging from 0.40 to 0.48, which is smaller than the I /Itypically 0.49 to 0.55 of conventional PVA fibers, thereby impartingenhanced orientation to the amorphous region of the fibers of thepresent invention as compared to conventional PVA fibers.

Many spinning methods have heretofore been developed for PVA fibers. Forexample, Wet-spinning through a coagulation bath containing sodiumsulfate, wet-spinning through a coagulation bath containing sodiumhydroxide, dry-spinning and the like. PVA fibers manufactured by theseconventional methods are characterized by a high degree ofcrystallization, with the Width of the crystals exceeding 95 A. Inparticular, PVA fibers manufactured by coagulation through a causticsoda bath exhibit a [3 value of below 0.83, and a crystal width of about120 A. Thus, the conventional PVA fibers are characterized by thoroughdevelopment of the crystal width; whereas, in the PVA fibers of thepresent invention containing 0.2 to 0.9% of boric acid, and preferably0.2 to 0.7% of boric acid, the crystals do not develop along the widedirection and so the width of the crystals is merely 55 to 82 A.

In conventional PVA fibers, the length of the molecular chains of theamorphous region are irregular and scarcely oriented; hence, thestructure thereof is random and loose. The structural parameter I /I ofsaid conventional PVA fibers having such an irregular amorphous regionranges from 0.49 to 0.55.

In contrast, however, the PVA fibers of the present invention containingboric acid, a part of which cross links With the PVA molecule impartingdifficulty in movement of the molecular chain, thereby providingconsiderable orientation in the amorphous region of the PVA moleculegiving rise to a compact structure, exhibit a value of I /Im below 0.48.

The excellent strength and the high temperature performance of thefibers of the present invention are considered to depend largely on thestructure of the amorphous region thereof.

The novel synthetic fibers of the present invention are highlycrystallized and highly oriented. These fibers are characterized byexhibiting a yarn dry break strength at room temperature of at leastg./d., a microcrystal length (half width of the reflection along (020)plane) of at least 125 A. and containing 0.2 to 0.9 weight percent basedon PVA of boric acid (H BO or a borate salt thereof.

The fibers of the present invention exhibit markedly improvedperformance at high temperatures, thus, for example, the yarn dry breakstrength at 120 C. is maintained at at least 7.5 g./d., the initialmodulus at 120 C. is maintained at at least g./d., and the yarn creep at135 C. is less than 2%.

In general, the elongation of break of a synthetic fiber increases withthe rise in the temperature, while both the break strength and theinitial modulus tend to decrease, the reason for which can be postulatedas follows; on heating, molecular chains existing in the looselyoriented regions of the fiber begin to move, the motion imparted to themolecular chains by heating propagates gradually to the highly orientedregions, resulting in a loosely oriented structure of the fiber as awhole. As a consequence, it is essential to inhibit the movement of themolecular chains as much as possible. There are two possible ways tohalt molecular motion: (1) by imparting extremely high orientation tothe molecular chain, the whole molecular chain becomes immobile, or (2)by adding certain materials which suppress the motion of the molecularchain. However, neither method alone can improve both the break strengthand the initial modulus at high temperatures which are the principalobject of the present invention.

Conventional post-treatment of the fiber with boric acid provides someimprovement of the initial modulus; however, the break strength isinevitably lowered to a considerable extent thereby. For example, theLatour Patent, US. 2,716,049, discloses a method of preparing PVA fiberconsisting of spinning a solution of 82-94% saponified PVA into acoagulation bath and post-treating the fiber with boric acid. The PVAfiber produced by the process of this patent exhibits a tenacity of2-3.4 g./d. and is soluble in water. In addition, it has been found thatPVA fibers produced by this technique exhibit a yarn tenacity of 1.50g./d., an elongation of 24.2% and a yarn initial modulus of 3.54 g./d.,all measured at C. In comparison, the PVA fibers of the presentinvention exhibit a yarn tenacity of more than 7.5 g./d. at 120 C., ayarn modulus of more than 100 g./d. at 120 C., and are essentiallyinsoluble in water.

It has now been found that a fiber structure with markedly highorientation in the crystalline regions and containing boric acid or aborate salt to suppress the motion of the molecular chain in theamorphous regions is effective in achieving the purposes of the presentinvention. A part of or all the boric acid or borate salt combines withPVA in the loosely oriented regions of the fiber to suppress the motionof the molecular chain imparted thereto by heating. If the content ofboric acid is less than 0.2%, it is insufficient to inhibit suchmolecular motion; while use of amounts of said boric acid exceeding0.9%, precludes high orientation of the molecular chains resulting in alowering of the tenacity or break strength. The break strength of thePVA yarn of the present invention at room temperature is at least 10g./d. which indicates that all the molecular chains of the PVA fiber ofthe present invention are highly oriented to attain such a highstrength.

The PVA employed in the present invention has an average degree ofpolymerization ranging from 1200 to 3500, and preferably ranges from1500 to 3000. As the average degree of polymerization decreases below1200, the viscosity of the spinning solution becomes too low to effectstable spinning of the solution and the resulting fibers exhibitinsufiicient strength. If the average degree of polymerization is higherthan 3500, however, difiiculties are encountered in the spinningoperation which make the manufacture of good fibers extremely difiicult.The PVA employed in the present invention exhibits an initial degree ofsaponification of from 97 to 99.9%; however, the PVA in the fiber issubstantially completely saponified since additional saponificationoccurs during the fiber-forming process.

The PVA fibers of the present invention can be produced by a processcomprising: preparing an aqueous solution of PVA which contains boricacid or borate salt thereof (the spinning solution); spinning in acoagulating bath comprising a major amount of water, sodium hydroxide orpotassium hydroxide and sodium sulfate, said materials being present inthe coagulating bath in a predetermined amount; drawing the resultingfibers between rollers; neutralizing any alkali adhered to the fiberswith acid; wet-heat drawing of the fibers; water-rinsing to adjust theamount of boric acid remaining in the fiber to be within a predeterminedrange; dehydrating and drying; and, dry-heat drawing.

The concentration of the coagulating bath, which has heretofore beenused in the conventional wet spinning method to produce PVA fiberscontaining no boric acid or borate, is almost saturated with sodiumsulfate, when sodium sulfate is used as the dehydrating salt in thebath. This is done because the fibers will stick to one another due toinsufficient coagulation, when the concentration of the dehydrating saltin said bath is lower than 100 gm./l. Accordingly, the coagulating bathused in the present invention is further combined with sodium hydroxideor potassium hydroxide in a predetermined amount, thereby facilitatingthe spinning of spinning solutions containing boric acid or borate. Theproperties of the PVA fiber thus produced depend very little on thetemperature. It is often observed that when the content of sodiumsulfate is high in the coagulating bath, the drawability of the producttends to decrease. The PVA synthetic fibers produced in accordance withthe present invention exhibit superior drawability and less temperaturedependency as compared with conventional PVA fibers which contain noboric acid.

In accordance with the present invention, it has been found that theaqueous spinning solution of PVA containing boric acid or a watersoluble borate salt thereof can be coagulated to produce PVA syntheticfibers hav ng yarn tenacity, yarn initial modulus and yarn creep whrchhardly depend on the temperature. The method of the present inventioncomprises spinning an aqueous solution of PVA containing boric acid or aborate salt thereof into a coagulating bath being kept strongly alkalineby theaddition of to 100 gm./l. sodium hydroxide or potassium hydroxideand 100 to 330 gm./l. sodium sulfate, which then subjected to subsequenttreatments such as roller drawing, alkali neutralization, water-rinsingto adjust the residue of boric acid in the fiber to a range of 0.2 to0.9% by weight of PVA, and preferably to a range of 0.2 to 0.7% byweight of PVA, dehydration and drying, and dryheat drawing.

It is preferable to add boric acid or a water soluble borate saltthereof to the spinning solution in an amount ranging between 1 and 5%by weight of PVA.

Boric acid or any water soluble borate salt thereof can be employed inaccordance with the present invention. Any borate salt which isrelatively soluble in the aqueous spinning solution can be suitablyemployed, as for example, the alkali metal borates such as sodiumborate, po tassium borate and the like. The solution is maintainedweakly acidic, specifically between pH 3 and pH 5. The pH of thesolution can be regulated, if necessary, by addition of an acid thereto.Acids which can be added to the solution can be, for example, aninorganic acid such as sulfuric, hydrochloric and nitric acid, anorganic acid such as acetic acid, tartaric acid, etc.; or a combinationof an organic acid and a salt of an organic acid, e.g. citric acid andsodium citrate, acetic acid and sodium acetate, tartaric acid andpotassium tartaric acid and sodium citrate, etc.

When the spinning solution has a pH lower than 3, the rate ofcoagulation in the coagulating bath will be slower, and corrosion of theapparatus occurs due to the high acidity. On the other hand, when the pHis higher than 5, the solution becomes unstable causing an increase 6 inviscosity thereby greatly damaging the spinning conditions.

The concentration of PVA in the spinning solution preferably rangesbetween 10 and 30% by weight. The spinning solution is spun into astrongly alkaline coagulating bath containing mainly water and sodiumhydroxide or potassium hydroxide in a range of 10 to g./l. and sodiumsulfate in a range of 100 to 330 g./l. Sodium hydroxide or potassiumhydroxide concentrations of less than 10 g./l. result in unfavorableeffects such as reduction in the coagulating rate and reduction ofdrawability at the time of spinning. It is considered undesirable toexceed a sodium hydroxide or potassium hydroxide concentration of 100g./l. because gelling action due to alkali becomes so active, as todecrease the spinnability of the spinning solution causing suchproperties as the yarn tenacity, yarn initial modulus and yarn creep tobe inferior. When the concentration of sodium sulfate is less than 100g./l., gelling action due to alkali overpowers the dehydration andcoagulating action of the sodium sulfate. This causes swelling of thefiber at the time of co agulation, which adversely affects the qualityof the product. On the other hand, concentrations of sodium sulfateexceeding 330 g./l. cause deformation in the fibers cross section tosubstantially an elliptical cross section since dehydration andcoagulating action overpowers other actions. The deformed section of thefiber is a cause of reduction in drawability.

In the present invention the PVA fiber thus spun is subjected tosubsequent conventional treatments such as roller drawing,neutralization of alkali by the use of acid, wet-heat drawing, and isthen water-rinsed to adjust the amount of boric acid remaining in thefiber to be in a range of 0.2 to 0.9% by weight of PVA. The residue ofboric acid after water-rinsing should be more than 0.2% by weight of PVAbecause swelling of the fiber at the time of rinsing may occur when itis less than said amount. The swelling of the fiber will cause a slackin the fiber, which can then be caught in the rollers resulting in anunstable operation, thereby decreasing such properties as the yarntenacity, yarn initial modulus and yarn creep.

These drawbacks are not observed in the present invention because theresidue of boric acid present in the fiber may either react with PVA toeffect formation of interor intra-molecular cross linkings, hang on thePVA chains, or remain unreacted. This is one of the characteristicfeatures of the present invention. When the amount of said boric acidexceeds 0.9% by weight, the drawability of the fiber will decreaseresulting in a decrease in the absolute values of the yarn tenacity andyarn initial modulus.

Thus, by selecting the optimum conditions for coagulation, the processcan be stabilized for production of fibers having high drawability.Moreover, by so determining the conditions for water-rinsing as tomaintain the residue of boric acid in the range of 0.2 to 0.9 weightpercent and preferably in the range of 0.2 to 0.7 weight percent,products having properties hardly dependent on temperature are obtainedwithout reducing the dry-heat drawability.

In the present invention, it is necessary to conduct the dry-heatdrawing of the PVA fiber subsequent to waterrinsing, dehydration anddrying, in order to achieve a total drawing ratio of more than 1300%. Ifthe total drawing ratio is less than 1300%, it is difiicult to obtainPVA fiber exhibiting the above-mentioned properties. According to thisinvention, the PVA fiber can be drawn to a total drawing ratio of 1800%.

The properties of PVA fiber thus obtained are: yarn tenacity at C. of atleast 7.5 gms./denier (g./d.); yarn initialy modulus at 120 C. of atleast 100 g./d.; and yarn creep at C. of less than 2% (elongation rateunder the load of 1 g./d. for 60 minutes). The fibers contain 0.2 to0.9% of boric acid or a borate salt. The

fibers of the present invention are superior to conventional PVA fiberscontaining no boric acid or borate with respect to high temperatureproperties.

The measurement of boric acid remaining in the synthetic fiber can beconducted in accordance with the following method:

A fiber weighing in terms of PVA approximately 2 g. is placed in acrucible, to which is added 0.1 mole/l. aqueous sodium hydroxidesolution to cover the fiber. After placing the crucible in a dryer at105 C. for one night, it is baked in an electric furnace at 400 C. to500 C. for 60 minutes. The fiber in the crucible is then placed in abeaker, to which is added ion-exchanging water and maintained as it isfor 60 minutes. A few drops of phenolphthalein indicator are added tothe beaker. Whereupon, 0.1 mole/1. hydrochloric acid is added until thecolor turns from red to yellow. After boiling for 30 to 60 minutes, itis cooled and neutralized to pH 7 by sodium hydroxide or hydrochloricacid addition as may be required. Mannite is added to the beaker and thesolution is again neutralized to pH 7 by titrating with 0.1 mole/l.sodium hydroxide. The volume (cc.) being titrated is measured. Theamount of boric acid remaining in the fiber is calculated by thefollowing equation wherein W(g.) is the weight of PVA in the testproduct measured in accordance with the method given above, and f andv(cc.) are the strength and the titrated volume, respectively, of the0.1 mole aqueous solution of sodium hydroxide:

The dry break strength or tenacity is determined according to JISL 1070.Thus the sample of the fiber is twisted 8 times per 10 cm., dried at 105C., for 3 hours and then immediately tested for break strength with asample having a length of cm., at a drawing speed 10 cm./min., using aconstant speed elongating tensile strength tester which has polyurethanefilm at the jaw face of the fastener.

The initial modulus can be obtained from the stressstrain curve given bythe determination of the above dry break strength, in reference to I ISL 1073. For the determination at room temperature, it is carried out ina room kept at 20 C., while for the determination at high temperatures,the upper and lower fastener of the tester is in an atmosphere of anelectric oven kept at 120 C. and the test performed until breaking ofthe sample occurs.

The determination of the halfwidth ,6 in the equatorial X-rayreflection, and the azimuthal X-ray intensity dis tribution I /I will beillustrated below.

(1) Equatorial X-ray reflection.--A sample of about 125 mg. and of 2.5cm. is made into a strip of 10 mm. in width, and then subjected to thescanning test at the equator thereof using a wide angle X-rayditfractomer, type D3F of Rigaku Denki Co. Ltd. under the conditions of40 kv., 15 ma., Cu-cathode, the line focus and the slits of 1/6, 0.3 mm.and 1/3.

(2) Length of the crystallite (half-Width of the reflection along (020)plane {3).-The same apparatus and sample as in (1) are used in thedetermination. Slit is 1 mm. pin hole collimator first slit 3 x 2, 2ndslit 1, as the incident slit, scanning slit 1. Recorder: range 250 c/Stime constant 2 sec., scanning speed 1/min., chart speed 1 cm./ min. Thehalf-width B of the reflection along (020) plane is measured from thedata obtained above, following a correction for the deviation ofinterference arising from the apparatus. From Table I below, the lengthof the crystallite in angstrom units can be calculated from (100/5).

(3) Determination of ti.-The half-width of the reflection along (100)reflection ,8 is determined as follows. A

TAB LE 1 Correction for deviation for apparatus interference inobtaining half- Width ([3) from apparent half-width (B) (4) AzimuthalX-ray intensity distribution.The scintillation counter is fixed at20=19.2 whereupon the azimuthal intensity distribution of reflection ismeasured by revolving the sample. It is measured by the number of countsper 2 minutes with the slit system of pin hole slit 3 x 3 cm., at 1, 2.

The PVA fiber of the present invention is characterized by having weakintensities along the azimuth angle of 6090. Though a shoulder near 60can be recognized, it is not significant, since reflections other thanthe amorphous scattering are included therein, as radial streaks can beseen in the X-ray photograph. The degree of orientation of the amorphousregion is consequently appropriately expressed by the ratio of theintensity along the meridian to that along 30 in the azimuth angle.

The following examples further define, describe and compare thepolyvinyl alcohol fibers of the present invention and their methods ofpreparation. Parts and percentages are by weight unless otherwiseindicated.

Example 1 10 kg. of an aqueous spinning solution containing 1.7 kg. ofPVA with a degree of polymerization of 1,750 and degree ofsaponification of 99.5 mole percent, and 34 g. of boric acid and asufficient amount of nitric acid to adjust the pH to 4.3 is prepared.The spinning solution is passed through spinning nozzles comprising 600spinning holes, 0.08 mm. in diameter into a coagulating bath containing30 g./l. of sodium hydroxide and 230 g./l. of sodium sulfate. The fiberthus spun is then taken out of the bath at a rate of 10 rn./min., andthen subjected to subse quent treatments such as; roller drawing ofneutralization in a bath comprising 70 g./l. of sulfuric acid and 300g./ 1. of sodium sulfate; wet-heat drawing of 150%; water-rinsing toadjust the amount of boric acid to be 0.45%; dehydration and drying; anddry-heat drawing of 220%. The final product obtained is drawn to a totaldrawing ratio of 1,500%.

The product thus obtained exhibits a yarn tenacity of 9.3 g./d. at C.,yarn initial modulus of g./d. at 120 C. and yarn creep of 1.4% at 135 C,and furthermore exhibits a {3 of 1.04 and IM/lgo of 0.44.

In Table 2 below, comparative examples are provided which illustrate theeffects on yarn properties of variations in process conditions and boricacid concentration. The conditions employed in Example I and theresulting yarn properties so obtained are also set forth to assist inthese comparlsons.

TABLE 2 Comparison Example Material:

Polymerization degree of PVA 1. 750 1,750 1, 750 1, 750 1,750 1, 750 1,750 1, 750

Saponification degree of PVA (mol percent) 99. 5 99.5 99. 5 99. 5 99. 599. 5 99. 5 99. 5

Spinning solution:

The concentration of PVA (percent) 17 17 17 17 17 18 18 17 The amount ofboric acid added (percent) 2. 2. 2 2. 2 2. 2 2. 2 2.6 2.6 2.0

p 4.3 4.1 4.1 4.1 4.1 4.0 4.0 4.3 Coagulation bath NaOH (g./l.) 30 8 1108O 15 40 40 30 NagSOq (EL/1.) 230 260 150 90 360 220 220 230Neutralization bath:

H250. (g./1.) 70 7O 70 70 80 80 NarSOi (g./1.) 300 300 300 300 320 320300 Drawing:

Total drawing ratio (percent) 1, 100

Roller drawing (percent) 100 Wet-heat drawing (percent) 150 Dry-heatdrawing (percent) 140 Amount of residue of boric acid (percent) 0. 46Tenacity (120 C.) (g./d.) 6. 5 Initial modulus (120 G.) (g /d) 96 Creep(135 C.) (percent). 2.3 9 0. 02 Ira/ a0 i151 1 'lartan'c acid used toadjust pH.

1 Acetic acid and sodium acetate used to adjust pH. 3 incapable of beingspun.

4 Sample exhibited poor drawability.

5 Sample exhibited poor spiuability.

NoTE.In Example 1 to comparative Example 4, nitric acid is used toadjust the pH.

EXAMPLE 2 PVA fiber containing sodium borate and drawn to a totaldrawing ratio of 1,500% is obtained in the same manner as in Example 1,except that sodium borate is employed in an amount of 1.5% of PVA inlieu of boric acid and tartaric acid is employed in lieu of nitric acidfor adjustment of pH. The product obtained exhibits a yarn tenacity of9.1 g./d. at 120 C., yarn initial modulus of 127 g./d. at 120 C., yarncreep of 1.5% at 135 C, a [3 of 0.98 and I /I of 0.48.

EXAMPLE 3 An aqueous PVA solution having a concentration of PVA ofweight percent and containing 150 g. of PVA with a degree ofpolymerization of 2,350 and a degree of saponification of 99.5 molepercent is admixed with g. of boric acid (2% by weight of PVA) and asmall amount of acetic acid to prepare a spinning solution of pH of 4.5.The spinning solution is spun into a strongly alkaline coagulating bathmainly of water containing g./l. of sodium hydroxide and 250 g./l. ofsodium sulfate. After taking the spun fibers out of the bath at a rate0f 10 m./min., they are subjected to roller drawing of 100%,neutralization, wet-heat drawing of 150%, waterrinsing to adjust theamount of boric acid residue to 0.4% by weight of PVA, dehydration anddrying, and dry-heat drawing of 200%. The product (1,200 d./600 f.) isthus drawn to a total drawing ratio of 1,400%. The product thus obtainedexhibits a yarn tenacity of 9.2 g./d. at 120 C., yarn initial modulus of131 g./d. at 120 C., yarn creep of 1.9% at 135 C., a ,8 of 1.06 and I /Iof 0.47; the product is superior in its properties at high temperature.

EXAMPLE 4 An aqueous solution of PVA of 17 weight percent containing 100kg. of PVA with a degree of polymerization of 1,750 and a degree ofsaponification of 99.9 mole percent is admixed with 2 kg. of boric acid(2 weight percent of PVA) and 0.3 kg. of acetic acid (0.005 g.equivalent to PVA 100 g.) to prepare a spinning solution. The pH ismaintained at 4.5.

The spinning solution is passed through nozzles of 1,000 holes in numberand 0.15 mm. in diameter into the coagulating bath containing g./l. ofsodium hydroxide and 200 g./l. of sodium sulfate. Then, the fibers aretaken out of the bath at a rate of 10 m./min. The spinning condition isvery stable in this case; during two weeks spinning, no diflicultiessuch as clogging of the nozzles is observed. The fiber thus spun is thensubjected to the same processing as in Example 3; i.e., roller drawing,neutralization, wet-heat drawing, water-rinsing to adjust the amount ofresidual boric acid to 0.5% by weight of PVA, dehydration, drying, anddry-heat drawing. The product (1,800 d./1,000 f.) thus obtained is drawnto a total drawing ratio of 1,400%. The product exhibits a yarn tenacityof 9.3 g./d. at C., yarn initial modulus of 134 g./d. at 120 C., yarncreep of 1.8% at 135 C., a ,6 of 1.13 and I /I of 0.46.

EXAMPLE 5 1 kg. of an aqueous spinning solution containing g. of PVAwith a degree of polymerization of 1750 and degree of saponification of99.5 mol percent, 5.95 g. of boric acid (3.5 weight percent on PVA) andsulfuric acid sufiicicnt to adjust the pH to 4 is prepared. The spinningsolution is passed through a nozzle into a coagulation bath containing15 g./l. of sodium hydroxide and 230 g./l. of sodium sulfate. Theresultant fiber is subjected to the same subsequent treatment as inExample 1 to obtain PVA fiber containing 0.5 weight percent of boricacid.

The product thus obtained exhibits excellent properties at 120 C. and ap of 1.11 and I /I of 0.45.

Example 6 A PVA aqueous spinning solution containing 17 weight percentPVA with a degree of polymerization of 1700 and degree of saponificationof 99.5 mol percent, boric acid of 2 weight percent on PVA and nitricacid of 0.2 Weight percent on PVA to adjust the pH to 4 is prepared.

The spinning solution is passed through a conventional nozzle comprising600 holes into a coagulation bath at 40 C. containing 20 g./l. of sodiumhydroxide and 250 g./l. of sodium sulfate. The resultant fiber is rollerdrawn and then subjected to subsequent treatments such as:neutralization of sodium hydroxide on the fiber with an acid, wet-heatdrawing, Water-rinsing of the fiber to adjust the amount of boric acidin the fiber, drying and dry-heat drawing to a total draw ratio of13001500%.

In Table 3 below, the resultant PVA fibers containing various amounts ofboric acid are shown with their properties.

TABLE 3 The amount of boric acid contained in the fiber (percent/PVA) 0.21 0. 36 0.50 0. 67 0. 85 0. 95 1. 05 Total drawing ratio (percent) 1,200 1, 500 1,500 1, 500 1,500 1, 400 1, 200 1, 140 Dcner/filament 1,200/500 1, 200/600 1, 200/600 1, 200/600 1, 200/600 1, 280/600 1,480/600 1, 550/ n00 D ry breaking tenacity (g./d.) 9.7 11.2 11. 6 11.711.5 10.1 9.8 9.3 Iiitial modulus (g./d.) 230 240 245 250 247 236 210204 120 Dry breaking tenacity (g d 7.0 8.0 8.5 8. 7 8. 6 s. 5 7. 4 7. 3Initial modulus (g./d 70 101 115 120 127 122 96 95 1 0. 89 1. 06 1.12 1. l3 1. 22 1. 32 1. 34 1. 35 IM/Ian 0. 50 0. 46 0.48 0. 46 0.45 0.4S 0. 53 0. 54

Example 7 A PVA aqueous spinning solution containing 17 weight percentof PVA with a degree of polymerization of 1750 and a degree ofsaponification of 99.9 mol percent, 2.8 weight percent on PVA of boricacid and 0.24 weight percent on PVA of tartaric acid to adjust the pH to4 is prepared. The spinning solution is passed through the same nozzleas in Example 1, into a coagulation bath at 45 C. containing 30 g./l. ofsodium hydroxide and 225 g./l. of sodium sulfate. The resulting fiber isthen subjected to subsequent treatments such as: roller-drawing,neutralization of sodium hydroxide on the fiber with an acid, wet-heatdrawing, water-rinsing of the fiber to adjust the amount of boric acidto about 0.5%, drying and dry-heat drawing to a total draw ratio of1200- 1500%.

The properties of the fibers thus obtained are shown in Table 4 below.

TABLE 4 water insoluble polyvinyl alcohol having an average degree ofpolymerization of from about 1200 to 3500 and containing a residue ofboric acid or a water soluble borate salt thereof in an amount of from0.2 to 0.9% by weight of polyvinyl alcohol, said fibers beingcharacterized by a half-width of reflection (B) of 0.98 to 1.40 and an I/I of from 0.40 to 0.48 derived from the azimuthal X-ray intensitydistribution at the angle of diffraction of 19.2.

2. Polyvinyl alcohol fibers as defined in claim 1 exhibiting a:

yarn dry break strength at room temperature of at least 10 gut/denier;yarn tenacity at C. of at least 7.5 gm./denier; yarn initial modulus at120 C. of at least 100 gm./

denier, and yarn creep at C. of less than 2% 3. Polyvinyl alcohol fibersas defined in claim 1 containing a residue of boric acid or a watersoluble borate The amount of boric acid contained in the fiber(percent/PVA) 0. 46 O. 52 0.48 0. 50 Total drawing ratio (percent) 1,200 1, 350 1, 400 1, 500 Denci lerlfilament 1, 200/ 600 1, 200/ 600 1,200/ 600 1, 200/600 Dry breaking tenacity (g./d.) 9. 7 10. 1 11. 0 11.5120 I1ltlal modulus (g./d.) 232 230 245 260 m breaking tenacity (g./d.)7.0 8.0 8.2 s. 6 Initial modulus (g./d.) 75 102 109 127 0. 92 1. 01 1.08 1. 15 I'M/I30 0. 51 0. 47 0. 46 0. 44

The PVA synthetic fibers of the present invention which exhibitoutstanding properties at high temperature find Widespread application,for example, they can be employed in the tension member of V belts andfor reinforcement of hoses. The high modulus and low creep of the fibersof the present invention at high temperature enables the manufacture ofV belts exhibiting excellent dimensional stability under the conditionsof use. High pressure hoses employed in oil pressurized machines andtools will be greatly improved by the use of the PVA fibers of thepresent invention because the expansion of the hose against the innerpressure is kept very small by the high modulus of the present fibers athigh temperature.

Although specific materials and conditions were set forth in the aboveexemplary processes for preparing the outstanding polyvinyl alcoholfibers of the present invention, these are merely intended asillustrations of the present invention. Various other polyvinylalcohols, watersoluble borates and process conditions such as thoselisted above may be substituted in the examples with similar results.

Other modifications of the present invention will occur to those skilledin the art upon a reading of the present disclosure. These are intendedto be included Within the scope of this invention.

What is claimed is:

1. Polyvinyl alcohol fibers comprising an essentially salt thereof in anamount of from 0.2 to 0.7% by weight of polyvinyl alcohol.

References Cited UNITED STATES PATENTS 3,751,547 8/1973 Kawakami et al.264 2,072,302 3/ 1937 Hermann et al. 264185 2,072,303 3/ 1937 Hermann eta1. 264185 2,445,555 7/ 1948 Binda 26091.3 VA 2,716,049 8/1955 Latour264185 2,928,131 3/1960 Mahler 264343 3,167,604 1/1965 Arakawa et al.264185 3,170,973 2/1965 Tanabe et al 264185 3,365,527 1/1968 Tanabe eta1 264185 3,472,804 10/1969 Nobile et al. 264185 3,660,556 5/ 1972Ashikaga et a1 264185 FOREIGN PATENTS 2,061 4/1959 Japan 264---185 5,8226/1962 Japan 264185 14,422 7/1962 Japan 264185 166,444 12/1964 U.S.S.R.264185 JAY H. WOO, Primary Examiner US. Cl. X.R. 264-185 b 3 3 5 UNITEDSTATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent 3,850,901 DatedAugust 21, 1975 Inventor(s) ShOlChl Tanaka et al It is certified thaterror appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Col. 10, Table 2, 10th entry in the second column headed "ComparisonExample 1'': 1,100" should be read as "1,10o

I Col. 10, Table 2, 10th entry in the third column headed "ComparisonExample 2": 1,200" should be read as "l,200

Col. 10, Table 2, 10th entry in the fifth column headed "ComparisonExample 4": 1,000" should be read as "1,100

Signed and Bacaled this twenty-eight Day Of October 1975 E Attest:

RUTH C. MASON C. MARSHALL DANN 14118511718 ff Commissioner of Patentsand Trademarks L I .J

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTIQN Patent No.5, 5,90l Dated November 26, 197

Inventor(s) Shoiohi Tanaka et al It is certified that error appears inthe above-identified patent and that said Letters Patent are herebycorrected as shown below:

Col. 5, line 69: "tartrate, should be inserted after "potassium".

Col. 7, line 60: "ma" should be read as "mA".

Col. 7, line 61: "1/6" should be read as "l/6".

Col. 8, Table 1, third entry in the second column headed "B": "2" shouldbe read as "3".

Signed and sealed this 8th day of April 1975.

STE-.1) fittes C. PLQRSI K-"JTL DANE"? "TET C. "303-? Commissioner ofPatents Xttesting Officer and Trademarks FORM PC4050 (10-69) USCOMM-DC33754:

u,s. covzmmzm' rmm'ms owes: a 93 o

1. POLYVINYL ALCOHOL FIBERS COMPRISING AN ESSENTIALLY WATER ISOLUBLEPOLYVINYL ALCOHOL HAVING AN AVERAGE DEGREE OF POLYMERIIZATION OF FROMABOUT 1200 TO 3500 AND CONTAINING A RESIDUE OF BORIC ACID OR A WATERSOLUBLE BORATE SALT THEREOF IN AN AMOUNT OF FROM 0.2 TO 0.9% BY WEIGHTOF POLYVINYL ALCOHOL, SAID FIBERS BEING CHARACTERIZED BY A HALF-WIDTH OF(100) RELFACTION (B) OF 0.98 TO 1.40 AND AN IM/I30 OF FROM 0.40 TO 0.48DERIVED FROM THE AZIMUTHAL X-RAY INTENSITY DISTRIBUTION AT THE ANGLE OFDIFFRACTION OF 19.2*.